Some random generators in ruby based on Coursera reactive programming course

random_generators.rb

module Generators
  module Utils
    def self.included(other)
      other.extend(ModuleMethods)
    end

    module ModuleMethods
      def arbitrary
        @arbitrary ||= {}.tap do |o|
          o[Integer] = ->{Random.rand(-1e+10..1e+10).to_i}
          o[Boolean] = ->{o[Integer] > 0}
        end
      end

      def integers
        arbitrary[Integer].call
      end

      def booleans
        arbitrary[Boolean].call
      end

      def choose(lo, hi)
        lo + integers  % (hi - lo)
      end

      def one_of(*xs)
        xs[choose(0, xs.length)].call
      end

      class Boolean; end
    end
  end

  module Arrays
    include Utils

    def self.generate
      one_of(->{[]}, ->{generate.push(integers)})
    end
  end

  module Trees
    include Utils

    def self.generate
      self.one_of(->{Leaf.new(integers)}, ->{Node.new(generate, generate)})
    end

    class Leaf
      def initialize(x)
        @x = x
      end

      def to_s
        "(#{@x})"
      end
    end

    class Node
      def initialize(l, r)
        @l = l
        @r = r
      end

      def to_s
        "(#{@l} . #{@r})"
      end
    end
  end

  module Lists
    include Utils

    def self.generate
      one_of(->{List.new(nil)}, ->{generate.cons(integers)})
    end

    class List
      attr_accessor :head, :tail
      def initialize(*xs)
        @head = xs.first
        @tail = List.new(*xs[1..-1]) if xs.any?
      end

      def cons(x)
        l = List.new(x)
        l.tail = self
        l
      end

      def to_s
        "(#{@head} #{@tail})"
      end
    end
  end
end